It is possible that the main title of the report Marfan Syndrome is not the name you expected. Please check the synonyms listing to find the alternate name(s) and disorder subdivision(s) covered by this report.
As Jenny points out, being able to lisp the alphabet song at age two has little to do with 'knowing' the alphabet. And, yes, most children learn the letters by sight and sound in kindergarten, although most are capable of learning this information sooner if diligently taught by parents or others.
Before children learn to use the alphabet, they employ a default strategy of attaching a visual cue to meaning. This visual cue strategy explains why very young children can recognize many words in their normal surroundings, for example, reading McDonald's with the arches logo.